Generally, since brass alloys including JIS CAC 203 C3604 and C3771 are excellent in characteristics, such as corrosion resistance, machinability, mechanical properties, they have widely been used for tapwater plumbing equipment including valves, cocks and joints, and for electronic device parts. The brass alloys of this kind possibly induce stress corrosion cracks when having been exposed to a corrosion environment, such as an ammonia atmosphere, and loaded with a tensile stress. As a countermeasure for preventing stress corrosion cracking from occurring in the brass alloys, various proposals have heretofore been made.
A brass material of Patent Document 1, for example, contains 57 to 61% of Cu and 1 to 3.7% of Pb, has an Sn content of 0.35% or less, and is brass comprising two phases of α+β at normal temperature. This brass has an α-phase average grain size of 15 μm or less, a β-phase average grain size of 10 μm or less and an α-phase ratio exceeding 80% to intend to enhance the stress corrosion cracking resistance.
Patent Document 2 proposes brass having a crystalline structure of α+β+γ at normal temperature, an α-phase area ratio of 40 to 94% and respective β-phase and γ-phase area ratios of 3 to 30% at normal temperature, respective α-phase and β-phase average grain sizes of 15 μm or less and γ-phase average grain minor axis of 8 μm or less, containing 8% or more of Sn in the γ phase and having the β phase surrounded by the γ phase. This brass also intends to enhance the stress corrosion cracking resistance because of the high Sn content and contains 1.5 to 2.4 wt % of Pb.
Patent Document 1: JP-A 2006-9053
Patent Document 2: Japanese Patent No. 3303301